A wide variety of inorganic and organic pigments are used in the art to impart bright yellow shades to coating compositions designed for interior or exterior surfaces. The most widely used inorganic yellow pigment is chrome yellow, a primrose yellow shade of lead chromate, referred to in the "Color Index" under the designation Lead Sulfochromate CI-77603. Primrose chrome yellow is generally characterized by good color strength and bleed resistance, but suffers from poor lightfastness relative to commonly used organic yellow pigments.
Among the organic yellow pigments, yellow azo pigments prepared by coupling diazotized amines with a variety of coupling compounds are most commonly used. Two well-recognized types of azo yellow pigments have become established in the trade. The first type, known as "toluidine yellows" since a well-known member of the series is obtained by coupling a nitrotoluidine (3-nitro-4-amino toluene) with actoacetanilide, is generally characterized by moderate color strength and good light-fastness, but poor bleed resistance. One of the toluidine yellows, prepared from coupling diazotized 2-nitro-4-chloroaniline with acetoacet-o-chloroanilide, exhibits superior color strength and lightfastness, but comparably poor bleed resistance. The second type of product, known as "benzidine yellows" is prepared by coupling of tetrazotized derivatives of benzidine (4,4'-diaminobiphenyl) coupled with derivatives of acetoacetanilide. Benzidine yellows exhibit color strength in the order of at least two times that commonly found in the toluidine yellows but have suffered from the defect of poor lightfastness.
The art has long recognized the need for a yellow pigment which exhibits the color strength and lightfastness of the azo yellows in combination with the bleed resistance of the chrome yellows. One attempt to fill this need is disclosed in Johnson U.S. Pat. No. 3,032,546. This patent describes a yellow azo pigment, prepared by coupling diazotized 5-nitro-2-aminoanisole with acetoacet-o-anisidide, having high color strength good lightfastness, and improved bleed resistance. However, Johnson teaches that although this pigment exhibits less bleeding in conventional enamels and water-based paints than prior art toluidine yellows, it is still not free from bleeding and, consequently, must be used with caution whenever paints of different colors are being used at the same time.
This invention provides for new azo pigments having color strength and lightfastness comparable to commonly used organic yellow pigments coupled with the bleed resistance possessed by the chrome yellow pigments.